In recent years, people with diabetes have typically measured their blood glucose level by lancing a fingertip or other body location to draw blood, applying the blood to a disposable test strip in a hand-held meter and allowing the meter and strip to perform an electrochemical test of the blood to determine the current glucose concentration. Such discrete, in vitro testing is typically conducted at least several times per day. Continuous in vivo glucose monitoring devices are currently being developed to replace in vitro devices. Some of these continuous systems employ a disposable, transcutaneous sensor that is inserted into the skin to measure glucose concentrations in interstitial fluid. A portion of the sensor protrudes from the skin and is coupled with a durable controller and transmitter unit that is attached to the skin with adhesive. A wireless handheld unit is used in combination with the skin-mounted transmitter and sensor to receive glucose readings periodically, such as once a minute. Every three, five or seven days, the disposable sensor is removed and replaced with a fresh sensor which is again coupled to the reusable controller and transmitter unit. With this arrangement, a person with diabetes may continuously monitor their glucose level with the handheld unit. Detailed descriptions of such a continuous glucose monitoring system and its use are provided in U.S. Pat. No. 6,175,752, issued to Abbott Diabetes Care Inc., formerly known as TheraSense, Inc. on Jan. 16, 2001, which is incorporated by reference herein in its entirety.
Transcutaneous analyte sensors may be inserted into the user's skin using an automatic introducer or inserter device, such as those described in U.S. patent application Ser. No. 10/703,214, published Jul. 8, 2004 under publication number 2004/0133164, now U.S. Pat. No. 7,381,184, incorporated herein by reference in its entirety. Most sensor inserter devices described in the above published patent application have two springs, one for driving an introducer sharp and a sensor into the skin of a patient, and another for retracting the introducer sharp, leaving the sensor behind in the patient's skin. The spring arrangements are chosen to provide an introducer sharp and sensor speed optimized to insert the sensor into a typical patient.